The present invention relates to methods and compositions for improving the adherence of polymer gels to surfaces, particularly tissue surfaces, and for improving the compliance of the materials.
Locally polymerized gels have been used as barriers and drug delivery devices for several medical conditions. Adherence of the formed gel to the tissue can be a problem, especially under surgical conditions, where the tissue surface to be treated is typically wet, and may further be covered with blood, mucus or other secretions. Hubbell and co-workers have described two methods for photopolymerizing gels in contact with tissue surfaces. In U.S. Pat. No. 5,410,016, hereby incorporated by reference, application of biodegradable macromers to tissue, followed by photopolymerization to form a gel, is described. Two methods for photopolymerizing gels are described. In “bulk” polymerization, a suitable photoinitiator and accessory reagents are solubilized or dispersed in a solution of gelling macromers. On application of light, the entire solution volume crosslinks to form a gel which acts as a local barrier or drug depot. These gels have substantial adherence to most surfaces, including tissue surfaces which are merely moist. However, if a confounding layer of fluid is present on the surface when the macromer/initiator solution is applied, then the gel may delaminate from the surface after its formation.
An alternative way of forming a gel layer on a surface, as described in U.S. Ser. No. 08/024,657, which is hereby incorporated herein by reference, is called the “interfacial” method. In this method, the surface to be coated is treated with a photoinitiator which adsorbs or absorbs to the surface. After washing away excess, unabsorbed photoinitiator, a polymerizable macromer solution is applied to the surface. On exposure to light, polymerization is initiated at the surface, and progresses outward into the solution to the limit of diffusion of the photoinitiator-generated radicals during their lifespan. Coating thicknesses of up to about 500 micrometers (microns) are routinely obtained. Since they are in effect “grown” from the tissue surface, such gel layers have excellent adhesion to the tissue surface under difficult conditions, including the presence of thin layers of fluid adherent to the surface. The limited thickness of such interfacial gels is desirable in some circumstances, but represents a major limitation where gels of substantially greater thickness than 500 microns are required, for example, for use in drug delivery, or in forming a thick physical barrier between the tissue surface and its surroundings. In addition to the photopolymerizable gels described by Hubbell et al (WO 93/17669) and Sawhney et al., (J. Biomed. Mats. Res. 28, 831–838, 1994), systems for forming drug delivery depots or barriers on surfaces include the polymers described in U.S. Pat. No. 4,938,763 to Dunn, et al., U.S. Pat. Nos. 5,100,992 and 4,826,945 to Cohn et al., U.S. Pat. Nos. 4,741,872 and 5,160,745 to De Luca et al., and U.S. Pat. No. 4,511,478 to Nowinski et al. Use of preformed barrier materials such as Goretex™ membrane (W. L. Gore) has been described in the literature.
Although all of these materials are suitable for application to tissue and other substrates, adhesion is in many cases limited, or in the case of the preformed barrier materials, essentially non-existent.
There are many situations in which the application of a polymeric material, or a polymerizable material followed by polymerization, is the appropriate or preferred method of sealing a tissue or organ to prevent migration of a fluid, such as blood or air, from or into the tissue or organ.
Well-known materials for making such bonds are cyanoacrylate-based adhesives and fibrin glue. Cyanoacrylates are chemically related to familiar domestic adhesives such as “CrazyGlue™”. On contact with water, the cyanoacrylate residues spontaneously polymerize. The resulting resins are brittle, poorly biodegradable, and often not biocompatible.
Fibrin glues are typically made by contacting a solution or suspension of the blood protein fibrinogen with an enzyme or other reagent which can crosslink it. Typically, the enzyme thrombin is used, which cleaves the fibrinogen molecule, forming fibrin monomer which then spontaneously polymerizes. This is a natural reaction involved in the formation of blood clots. Fibrin glues often have better adherence to tissues than do cyanoacrylates, and are rapidly biodegraded. However, like cyanoacrylates, they have little flexibility or elasticity once their deposition is complete. A familiar example of a crosslinked fibrin-based material is a scab or an eschar.
Neither fibrin glues nor cyanoacrylates are stretchable, once polymerized. It is believed that this lack of compliance (i.e., high elastic modulus and low elongation at rupture) is an important reason why seals formed with these and related prior-art materials are likely to fail prematurely, especially when the area which is joined or sealed is subject to deformation.
Numerous materials are known and used in medicine which are highly elastic, such as rubber gloves and flexible elastic bandages. However, such materials do not bind tightly to tissue, particularly to moist tissue, which is required if the tissue is to be sealed.
It is therefore an object of the present invention to provide methods and compositions for enhancing the adhesion of polymeric materials to tissue surfaces and other substrates.
It is a further object of the present invention to provide methods and compositions for increasing the thicknesses of polymeric materials which can be “tethered” to a tissue surface or other substrates.
It is a further object of the present invention to provide improved initiator systems for the formation of gels on tissues and other surfaces.
It is a further object of the present invention to provide improved methods and new medical indications for the sealing and coating of tissue.
It is another object of the invention to provide an improved sealing material and method, characterized in that the sealant material is compliant with tissue after its formation, as well as strongly adherent to tissue.
It is a further object of the invention to provide kits for the formation of such compliant sealant materials.